/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util.xml;

import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;

import org.springframework.util.Assert;

/**
 * Contains common behavior relating to {@link javax.xml.transform.Transformer Transformers}
 * and the {@code javax.xml.transform} package in general.
 *
 * @author Rick Evans
 * @author Juergen Hoeller
 * @since 2.5.5
 */
public abstract class TransformerUtils {

    /**
     * The indent amount of characters if {@link #enableIndenting indenting is enabled}.
     * <p>Defaults to "2".
     */
    public static final int DEFAULT_INDENT_AMOUNT = 2;


    /**
     * Enable indenting for the supplied {@link javax.xml.transform.Transformer}.
     * <p>If the underlying XSLT engine is Xalan, then the special output key {@code indent-amount}
     * will be also be set to a value of {@link #DEFAULT_INDENT_AMOUNT} characters.
     *
     * @param transformer the target transformer
     * @see javax.xml.transform.Transformer#setOutputProperty(String, String)
     * @see javax.xml.transform.OutputKeys#INDENT
     */
    public static void enableIndenting(Transformer transformer) {
        enableIndenting(transformer, DEFAULT_INDENT_AMOUNT);
    }

    /**
     * Enable indenting for the supplied {@link javax.xml.transform.Transformer}.
     * <p>If the underlying XSLT engine is Xalan, then the special output key {@code indent-amount}
     * will be also be set to a value of {@link #DEFAULT_INDENT_AMOUNT} characters.
     *
     * @param transformer the target transformer
     * @param indentAmount the size of the indent (2 characters, 3 characters, etc)
     * @see javax.xml.transform.Transformer#setOutputProperty(String, String)
     * @see javax.xml.transform.OutputKeys#INDENT
     */
    public static void enableIndenting(Transformer transformer, int indentAmount) {
        Assert.notNull(transformer, "Transformer must not be null");
        if (indentAmount < 0) {
            throw new IllegalArgumentException("Invalid indent amount (must not be less than zero): " + indentAmount);
        }
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        try {
            // Xalan-specific, but this is the most common XSLT engine in any case
            transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", String.valueOf(indentAmount));
        } catch (IllegalArgumentException ignored) {
        }
    }

    /**
     * Disable indenting for the supplied {@link javax.xml.transform.Transformer}.
     *
     * @param transformer the target transformer
     * @see javax.xml.transform.OutputKeys#INDENT
     */
    public static void disableIndenting(Transformer transformer) {
        Assert.notNull(transformer, "Transformer must not be null");
        transformer.setOutputProperty(OutputKeys.INDENT, "no");
    }

}
